The atlas of lateral ventricle was generated using warping from the atlas of 1-year-old and then applied the morphological operation (e.g. dilation and erosion) in order to cover the whole ventricle area. The warping field was generated using ANTS. If you have a more suitable ventricle mask (e.g. the age or specific group matching), the more accurate esCSF would be obtained. For example, if your data set is fully matured age, you might be better using the own ventricle mask of that period. 

Best,
Sun Hyung